1998 Blazer Heat/AC Problem

I recently had problems with my heater core beingplugged up ....causing me to have no heat...I fixed that problem by flushing system...now I cannot shut the heat offMy a/c works fine lines cold under but it blows very hot air through the ventsIs there a door that won't open or is it the climate control knob..Was working fine before I flushed systemBurning hot in IndyTHANK YOU TO ALL

I have this EXACT same symptom with my daughter's Blazer. Flushed the heater core, and it suddenly went bonkers. I have the "computer controlled" version. I checked the actuator behind the glove box. It does not control the hot/cold mix. I have visited the Chevy dealer. They gave me a service bulletin number 1509645 that states that the actuator door is actually driven by an electrical motor. It says that you can "overdrive" the door past computer control, and must jumper something to get it to work. Now if I can just translate that. I'm going to search for more posts on this. Seems endemic. Hot in Texas

I've been dealing with this for a couple of weeks now on my 98 blazer. I have access to schematics and a scan tool which makes it a little easier. My experience has been with the automatic climate control system. I don't know very much about the manual control. There are several possible problems. The most likely, is that one of the gears in the blend door actuator is cracked. Therefore, the blend door is stuck in one position. The actuator CAN be accessed through the glove box but it is tight. On the left hand side you will see a vacuum controlled lever. That is for the defrost (if you turn the truck on and switch the vent position switch back and forth you will see it move). The blend door actuator is behind that so its easier to remove that vacuum diaphragm to gain access. The overdrive problem mentioned earlier could also be a problem. To reset this, turn the truck off, remove the RDO fuse for 30 seconds, replace the fuse, then turn the key to the run position. This will start a calibration cycle to reteach the computer where the maximum and minimum rotation points are so that it doesn't overdrive. If, after doing this procedure, the hvac system cycles back and forth from heat to cool there is probably a code set in the Climate Control Module and it may be time to get a dealer with a scan tool involved. On my truck and at least one other truck I have found out about, the control module is unable to sense the location of the actuator door (that is what causes it to "overdrive"). You can verify if your module is overdriving by removing the blend door actuator but leaving the electrical connector on. Turn the truck on, cycle to heat. The visible gear should rotate one direction then stop. Cycle to cool. The gear should rotate the other way and then stop. If it doesn't stop there may be something wrong with the control module. I hope this long-winded post helps someone.

I've been dealing with this for a couple of weeks now on my 98 blazer. I have access to schematics and a scan tool which makes it a little easier. My experience has been with the automatic climate control system. I don't know very much about the manual control. There are several possible problems. The most likely, is that one of the gears in the blend door actuator is cracked. Therefore, the blend door is stuck in one position. The actuator CAN be accessed through the glove box but it is tight. On the left hand side you will see a vacuum controlled lever. That is for the defrost (if you turn the truck on and switch the vent position switch back and forth you will see it move). The blend door actuator is behind that so its easier to remove that vacuum diaphragm to gain access. The overdrive problem mentioned earlier could also be a problem. To reset this, turn the truck off, remove the RDO fuse for 30 seconds, replace the fuse, then turn the key to the run position. This will start a calibration cycle to reteach the computer where the maximum and minimum rotation points are so that it doesn't overdrive. If, after doing this procedure, the hvac system cycles back and forth from heat to cool there is probably a code set in the Climate Control Module and it may be time to get a dealer with a scan tool involved. On my truck and at least one other truck I have found out about, the control module is unable to sense the location of the actuator door (that is what causes it to "overdrive"). You can verify if your module is overdriving by removing the blend door actuator but leaving the electrical connector on. Turn the truck on, cycle to heat. The visible gear should rotate one direction then stop. Cycle to cool. The gear should rotate the other way and then stop. If it doesn't stop there may be something wrong with the control module. I hope this long-winded post helps someone.

I purchased a new actuator and connected the electrical connector to it. It was immediately overdriven in one direction. What can I do to correct the problem with the climate control module?

I've been dealing with this for a couple of weeks now on my 98 blazer. I have access to schematics and a scan tool which makes it a little easier. My experience has been with the automatic climate control system. I don't know very much about the manual control. There are several possible problems. The most likely, is that one of the gears in the blend door actuator is cracked. Therefore, the blend door is stuck in one position. The actuator CAN be accessed through the glove box but it is tight. On the left hand side you will see a vacuum controlled lever. That is for the defrost (if you turn the truck on and switch the vent position switch back and forth you will see it move). The blend door actuator is behind that so its easier to remove that vacuum diaphragm to gain access. The overdrive problem mentioned earlier could also be a problem. To reset this, turn the truck off, remove the RDO fuse for 30 seconds, replace the fuse, then turn the key to the run position. This will start a calibration cycle to reteach the computer where the maximum and minimum rotation points are so that it doesn't overdrive. If, after doing this procedure, the hvac system cycles back and forth from heat to cool there is probably a code set in the Climate Control Module and it may be time to get a dealer with a scan tool involved. On my truck and at least one other truck I have found out about, the control module is unable to sense the location of the actuator door (that is what causes it to "overdrive"). You can verify if your module is overdriving by removing the blend door actuator but leaving the electrical connector on. Turn the truck on, cycle to heat. The visible gear should rotate one direction then stop. Cycle to cool. The gear should rotate the other way and then stop. If it doesn't stop there may be something wrong with the control module. I hope this long-winded post helps someone.

I removed the diaphragm but i cant get the actuator to seat and line up with the screw holes.

This same this happened to me today. The SES light came on, i took out the battery to reset the computer after doing some maintenance and my air doesn't work at all. I just had it serviced friday. The longer i have my blazer, the more i start to dislike it.

The AC was working great. The battery went dead. I replaced the battery. Now it only blows hot air. Mechanic just checked the AC and tried some "reset" things. He verified the AC compressor is blowing cold air, but doesn't know how to fix the problem. It's terribly hot in FL.

I have this EXACT same symptom with my daughter's Blazer. Flushed the heater core, and it suddenly went bonkers. I have the "computer controlled" version. I checked the actuator behind the glove box. It does not control the hot/cold mix. I have visited the Chevy dealer. They gave me a service bulletin number 1509645 that states that the actuator door is actually driven by an electrical motor. It says that you can "overdrive" the door past computer control, and must jumper something to get it to work. Now if I can just translate that. I'm going to search for more posts on this. Seems endemic.Hot in Texas

I've been dealing with this for a couple of weeks now on my 98 blazer.--- The overdrive problem mentioned earlier could also be a problem. To reset this, turn the truck off, remove the RDO fuse for 30 seconds, replace the fuse, then turn the key to the run position. This will start a calibration cycle to reteach the computer where the maximum and minimum rotation points are so that it doesn't overdrive. If, after doing this procedure, the hvac system cycles back and forth from heat to cool there is probably a code set in the Climate Control Module and it may be time to get a dealer with a scan tool involved.

I recently flushed mine and did the reset mentioned above. Ops check good.

Been driving for 3 winters with no heat! Thanks for the information! Saved me serious money.

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